If you want completely control your query build by Specification
with join fetch you can check CriteriaQuery
return type and change join fetch logic according to query type like this:
public class ContactSpecification implements Specification<Contact> {
@Override
public Predicate toPredicate(Root<Contact> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
if(query.getResultType() == Long.class) {
root.join(Contact_.company);
} else {
root.fetch(Contact_.company);
}
return cb.equal(root.get(Contact_.company).get(Company_.name), "Company 123");
}
}
I was not able to find this info in documentation, but from SimpleJpaRepository.getCountQuery()
method you can see query for count request first build for Long return type, and later fetch for expected class is running.
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaQuery<Long> query = builder.createQuery(Long.class);
Root<S> root = applySpecificationToCriteria(spec, domainClass, query);
It can be not reliable since it is an implementation details which can be changed, but it works.